The global disease burden due to leishmaniasis is high with as many as 12 million people currently infected, and 1-2 million new cases occurring each year, particularly in Africa, Asia and South America. It is considered as one of the least studied and most neglected of tropical diseases. The causative agent belongs to the genus Leishmania and it is transmitted via the bite of an infected phlebotomine sand fly. Over 20 species of Leishmania are known to cause diseases, which ranges from self-limiting cutaneous lesions to potentially fatal visceral disease, mainly depending on the causative parasite species. The most virulent form of disease is caused by L.donovani that is mostly prevalent in the Indian subcontinent and its pathogenetic mechanisms, particularly with regard to its phenotypic variants remain poorly understood. Sri Lanka is a new focus affected by leishmaniasis with the evidence gathered so far pointing towards the presence of genetically distinct strains of L.donovani that demonstrates an atypical phenotypic property of dermotropism, which is proposed here to be studied in depth using clinical, biological and latest molecular techniques. In depth understanding of such strain variations within the L.donovani species would enable better understanding of the virulent properties of this species and in turn would lead to the development of more efficient diagnostics and effective treatment methods in the future. The broad objective of this proposal is to study the phenotypic and genotypic characteristics of L.donovani that cause cutaneous leishmaniasis (CL) in Sri Lanka. Specifically, the essential dermotropic nature of the parasites will be determined through studies on the clinical/pathological sequelae of CL by long-term follow up of patients using clinical and serological criteria. Secondly, to study in vivo and in vitro correlates of parasite virulence, viz macrophage invasion and disease sequalae in established animal models. Thirdly, detailed genetic characterizations of local L.donovani strains is proposed to be done using Leishmania mini-circle DNA footprint assay, which has been established by the US collaborators, as an efficient and effective method to differentiate inter and intra-species sequence variations. Hence, this assay would enable in depth genetic characterization of parasite isolates that cause CL in Sri Lanka when analyzed together with similar data from strains that cause visceral disease in India and Nepal. Overall, this study is meant to enable better understanding of the pathogenicity of L.donovani, which in the long term would help reduce the global disease burden contributing positively towards the disease elimination efforts in the Indian subcontinent.